Method of producing magnetic materials



Patented June 24, 1930 UNITED STATES PATENT OFFICE PAUL STANGLIFF MOCANN, OF LA GRANGE, ILLINOIS, ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK METHOD OF PRODUCING MAGNETIC MATERIALS No Drawing.

This invention relates to improvements in the method of producing magnetic materials and has for its object the provision of an improved method for producing a magnetic material, particularly permalloy tape as a loading material for signalingconductors.

The word permalloy is used throughout this description to refer to alloys consisting chiefly of nickel and iron having high permeability at low magnetizing forces, such as the alloys described in patent to G. W. Elmen, Patent N 0. 1,586,887, issued June 1,

926. 1 In this patent the method of producing permalloy in the form of tape together with the method of applying it around an electrical conductor and then applying heat treatment thereto to build up high 5 permeability is disclosed. It is also pointed out therein that unless the tape has been hardened by work performed upon it after the last process anneal it will not have satisfactorily high permeability when it is applied to an electrical conductor. One of the reasons for the necessity of this mechanical condition in the metal is, as follows :When' the tape is mechanically hard it anneals at a lower temperature than when it is soft. Since the heat treatment which can be a plied to the tape is partly limited by t e lower melting point of the copper conductor on which the tape is applied and by other obvious conditions when a commercial process is desired, it can be seen that hard tape, being capable of heat treating at lower temperatures is much to be preferred to me.- chanically soft tape.

The method heretofore employed for producing the tape comprised alternatel annealing the stock and reducing the thic ness thereof by mechanical working, in each case the cooling following the annealing being comparatively slow. The final stage was one of mechanical working sufiicient to reduce the thickness by at least one-half, this final reduction having the effect of leaving the tape in a hard mechanical condition when finished. More specifically, the last process anneal was given to the tape when it was at a thickness of about .01' inch after Application filed November 6, 1924. Serial No. 748,043.

which the tape was cooled slowly and then reduced to .005. inch thickness in from eight to thirteen passes in a rolling mill, depending on the previous history of the tape and whether or not the tape was in the form of a wide strip which was subsequently cut to the proper width or in the form of a narrow strip, such as that obtained by the wire flattening process described in the patent reess anneal is therefore reduced. This quick cooling can be applied to permalloy tape which is being treated according to the strip method and according to the flattened wire method, and in each case beneficial results are obtained all in a manner which will be more fully explained hereinafter. The manner of cooling and the temperature from which quick cooling is to take place may vary over a wide range without departing y from the spirit and scope of the invention. The cooling should be as rapid as the condi-' tions existing will permit and the temperature from which the rapid cooling takes place should be at least as high as the magnetic transition temperature, about 600 0., but preferably slightly higher. Heating preliminary to rapid cooling should be at least to a temperature of 800 (3., but preferably higher, a temperature of 1200 (1., having been found to give very satisfactory results.

As has been indicated quick cooling, in order to give good results in the finished tape, must be followed by a mechanical working of the material treated, under normal conditions a 50% reduction in the thickness of the stock being sufficient to bring about suitable conditions in the material for building up a satisfactorily high permeability by a heat treatment as explained in detail in the patent referred to above. It is observed that, if rapid cooling takes place from a comparatively high temperature, the amount of work afterwards necessary to bring about the best metallurgical conditions in the tape will not be as great as when cooling takes place slow- 1y. When the tape has been reduced to its final size it is applied to the conductor and then heat treated in the manner disclosed in the patent referred to above.

/ As remarked above, the details of the meth= od may vary, depending upon whether the strip process of manufacture or the wire flattening process is employed. In order to explain these details they will be more fully referred to in connection with each of these methods of manufacture.

The details heretofore observed when the strip method of manufacture was employed consisted in casting the permalloy into a billet, rolling or swaging the billet to a sufiiciently small size so that it could be cold rolled and then cold rolling the stock so treated until the final thickness was reached, after which the strip was put through a slitting machine and cut into a plurality of strips of the width desired. The cold rolling was interspersed with annealing operations, the de- 7 tails of which consisted in rolling the strip onto a reeling device, placing it in an annealing pot, covering, and sealing the pot to prevent the flow of air into the pot while the metal was being cooled following the heating. The sealed pot was then placed in a furnace and raised to a high temperature after which it was removed and allowed to cool, the permalloy being left in the pot until a comparatively low temperature preferably not more than 260 C. was reached.

According to the present invention when the strip method of manufacture described in the preceding paragraph is used when the tape is being treated in the last pot anneal, the pot is allowed to cool gradually down to a sufliciently low temperature, about 600 (3., to prevent too rapid oxidation when the pot is opened. The cover is then raised very slightly so as to permit suflicient air to enter to cause a more rapid cooling of the stock, but not enough air to permit the degree of oxidation of the surface of the metal which would normally take place at this temperascribed above. When its reduction has been completed the tape is applied to a conductor to form an inductive loading therefor, and

is then heat treated while on the conductor in the manner described in the patent of G. W. Elmen referred to in the foregoing description.

When the wire flattening process was employed heretofore it was carried on in the following manner. The material was cast into the form of a billet and then either rolled or swaged until a sufliciently small size so that it could be drawn through the dies of a wire drawing mechanism. It was then drawn down to the diameter of about .051 after which it was flattened to form tape. Between the several wire drawing and wire flattening operations, the permalloy was annealed. in an annealing pot and cooled slowly thereafter.

According to the present invention, after the wire has been given the final anneal in the annealing pot it is cooled quickly in substantially the same manner and with the same result as when the strip type of manufacture described above is employed.

When the wire flattening type of manufacturing process is employed, instead of annealing the permalloy in pots, it may :be subjected to a continuous annealing process by being passed between electrical contact points, thereby being introduced into and simultaneously closing an electrical circuit so that the current, passing through the permalloy, will cause a heating up of the permalloy wire. Or as an alternative the wire may be passed through a tube or oven in which the requisite temperature is maintained. During the time that the wire is subjected to the electrical current or passed through the tube as described, it is preferably kept in a hydrogen atmosphere in order to prevent oxidation.

When this type of annealing is used the method for accomplishin a quick cooling will differ from that described above. A desirable and beneficial method is to pass the tape while still hot into a bath of water at room temperature. However, ,on account of the small size and relatively large surface of the ermalloy at this time in its manufacture su stantial quenching takes place when it is exposed to ordinary room atmosphere. The cooling should be at least as fast as 5 C. per second until the ta e has reached a temperature of 260 C. fter the above described cooling which follows the last rocess anneal the permalloy is reduced to its nal size, after which it may be applied to a conductor and then heat treated substantially as disclosed in the patent of G. W. Elmen referred to above, and as described briefly in preceding paragraphs herein.

Permalloy which has been rapidly cooled hardens more quickly than slow cooled tape,

as was explained above. For this reason the amount of work which must be performed upon the tape after the final heating, is reduced. For example, when slow coolin .is

employed hard tape with good permeabi ity is obtained by ma as described in the foregoing paragraphs the amount of work necessary 111 order to produce satisfactory tape is materially reduced as compared with previous methods of manufacture. Then, too, since the tape is mechanically hard the reduction may be accomplished in a fewer number of passes without deleteriously affecting the hardness and permeability of the finished tape.

\Vhen the method according to the present invention is employed the time required to manufacture the tape is materially reduced and the manufacturing process rendered more economical by reason of the smaller amount of time consumed and also because the apparatus required is in use for a shorter length of time.

What is claimed is:

' 1. A method of securing high permeability in magnetic materials which consists in heating the material to a temperature above 800 0., cooling quickly, performing work thereon to produce final thickness of the material, and then subjecting the material to a heat treatment determined by the hardness of the material to develop therein desirable magnetic properties.

2. A method of securing high permeability in permalloy loading tape, which consists in heating the material between 800 0. and

1200 0., cooling quickly, reducing the thickness of the tape, and then subjecting the tape after its application to a conductor to a predetermined temperature to impart to it desired magnetic properties.

3. A method of securing high permeability in permalloy loading tape which consists in heating the tape to a temperature approximately 1200 0., cooling quickly, reducing the thickness of the tape, placing the tape upon a signaling conductor to form an inductive loading therefor, and then applying heat treatment to the loaded conductor.

- 4. A method of securing high permeability in permalloy'loading tape which. consists in heating the tape to a temperature between 800 0. and 1200 0., quenching the tape in water, reducing the thickness of the tape, placing the tape upon a signaling conductor to form an inductive loading therefor, and then applying heat treatment to the loaded conductor. f I

5. A method of securing high permeability in permalloyloading tape which consists in heating the ta e to'a temperature above 800 0., cooling quickly from at least 600 0., reducing the thickness of the tape, placing the tape upon a signaling conductor to form an inductive loading therefor, and then applying heat treatment to the loaded conductor.

6. A method of securing high permeability in permalloy loading tape w ic heating the tape to a temperature of 1200 0., cooling quickly from at least 600 0., reducing the thickness of the tape, placing the tape upon a signaling conductor to form an inductive loading therefor, and then applying heat treatment to the loaded conductor.

7. A method of securing high permeability in permalloy loading tape which consists in heating the tape to a temperature of 1200 0., quenching in water, reducing by at least 40% the thickness of the tape, placing the tape upon a signaling conductor to form an inductive loading therefor, and subsequently applying heat treatment to the loaded conductor.

8. The steps in the treatmentof permalloy which comprise heating the permalloy to a temperature above 800 0., cooling quickly, and then reducing the size of the permalloy by mechanical working.

9. A method of treating magnetic materials, which consists in heating the material to a temperature between 800 0. and 1200 0., allowing said material to cool, first slowly and then quickly so as to develop therein de-v consists in sired magnetic properties, and then performing work thereon.

10. A method of treating magnetic materials, which consists in heating the material to a temperature between 800 0. and 1200 0., allowing said material to cool, first slowly to a temperature of approximately 600 0. I

and from that temperature quickly so as to develop therein desired magnetic properties, and then performing work thereon.

In witness whereof, I hereunto subscribe my vname this 29th day of October, A. D. 1924.

PAUL STANCLIFF MGCANN. 

